1. Field of the Invention
The present invention relates to methods for manufacturing nonreciprocal circuit devices such as isolators and circulators used in microwave bands, nonreciprocal circuit devices manufactured by the methods, and communication apparatuses incorporating the nonreciprocal circuit devices.
2. Description of the Related Art
Known nonreciprocal circuit devices having the following structures have a resin material arranged in a metal case.
Japanese Unexamined Patent Application Publication No. 10-242713 describes a nonreciprocal circuit device in which a resin film is formed at parts other than the connecting portions of the bottom of a metal case.
In addition, Japanese Unexamined Patent Application Publication No. 10-41706 describes a nonreciprocal circuit device having a metal case composed of an upper part and a lower part which includes an insulative resin.
These nonreciprocal circuit devices have the following problems to be solved.
Referring to FIGS. 12 and 13, a description will be given of the process of manufacturing each of the nonreciprocal circuit devices described in the related art.
FIG. 12 is a flowchart of the first manufacturing process.
As shown in FIG. 12, a resin material is formed in advance on the metal case. The resin layer is not formed in the process of assembling the nonreciprocal circuit device. Thus, the cost of the metal case increases and therefore the entire cost of the product also increases.
On the other hand, the method shown in FIG. 13 includes a step of heating a nonreciprocal circuit device in the assembling process to slightly demagnetize (anneal) the magnet.
FIG. 13 is a flowchart showing the process of manufacturing the nonreciprocal circuit device including the heating step.
In this process, as shown in FIG. 13, the nonreciprocal circuit device is heated after being assembled to perform partial thermal demagnetization of the magnet. This arrangement can prevent the deterioration of characteristics due to thermal demagnetization after the device is manufactured and sold.